The present disclosure relates to the useful manipulation of fluorescence found in substrates and particularly most paper substrates as commonly utilized in various printer and electrostatographic print environments. More particularly, the teachings provided herein relate to methods of providing fluorescent watermarks.
Watermarking is a common way to ensure security in digital documents. Many watermarking approaches exist with different trade-offs in cost, fragility, robustness, etc. One approach is to use ultra-violet (UV) fluorescent ink rendering, to encode a watermark that is not visible under normal illumination, but subsequently identify the presence or absence of the watermark in a proffered document using a standard UV lamp. However, these fluorescent inks are costly to employ, and thus are typically only economically viable in offset printing scenarios, and thus only truly avail themselves of long print runs. Additionally, these materials are often difficult to incorporate into standard electro-photographic or other non-impact printing systems like solid ink printers, either due to cost, availability or physical/chemical properties. This in turn discourages their use in variable data printing arrangements, such as for redeemable coupons, for but one example.
It is desirable to be able to detect the counterfeiting, illegal alteration, and/or copying of a document, most desirably in a manner that will provide document security and which is also applicable for digitally generated documents. It is desirable that such a solution also have minimum impact on system overhead requirements as well as minimal storage requirements in a digital processing and printing environment. Additionally, it is highly desirable that this solution be obtained without physical modification to the printing device and without the need for costly special materials and media.